Anybody running manual disc brakes? Pics

[Gregski]

Hi there in order to do some troubleshooting on my 1971 GMC 1/2 ton CORRECTION (71 cab on a 69 chassis) that came with factory drum brakes at all four corners that I have since converted to disc in the front I need to install a non power disk brake master cylinder and I would love to see some pics of how that mounts. My drum/drum setup was power so it had the big vacuum booster can on it

please and thank you

[dmjlambert]

1971 with drum brakes in front, I didn't know there was such a thing.

I have a 1969 C10, I put on it 1971 donor front disc brakes and spindles with new 1971-72 ball joints and steel brake tubing, and 1971 donor rear drum brakes and new 5-lug conversion rear axle shafts. I did manual brakes. The master cylinder bolts directly to the firewall.


http://www.67-72chevytrucks.com/vboard//showthread.php?p=9167631#post9167631

[lolife99]

1971 was the first year of disc brakes in all the trucks. There were many trucks with manual disc brakes from the factory.

[dmjlambert]

Yes that is what I thought, and I didn't know front drum brakes were an option for 1971. Gregski may have had the only one. Or it may be a GMC thing.

[Gregski]

Originally Posted by dmjlambert

1971 with drum brakes in front, I didn't know there was such a thing.

I have a 1969 C10, I put on it 1971 donor front disc brakes and spindles with new 1971-72 ball joints and steel brake tubing, and 1971 donor rear drum brakes and new 5-lug conversion rear axle shafts. I did manual brakes. The master cylinder bolts directly to the firewall.


http://www.67-72chevytrucks.com/vboard//showthread.php?p=9167631#post9167631

1,000 Super Thanks, this is exactly what I needed to see, shoot I forgot about the proportioning block I bet its a different one for drum/drum vs disc/drum

[Gregski]

Originally Posted by dmjlambert

Yes that is what I thought, and I didn't know front drum brakes were an option for 1971. Gregski may have had the only one. Or it may be a GMC thing.

sorry its a 71 cab on a 69 chassis, it's been a while since I wrenched on it, please check out this thread:

"Drum to Disc" conversions 67-70 pics and videos

[KQQL IT]

I do on my squarebody. Master from a '84 with manual brakes.
Aluminum master plastic reservoir

[jocko]

yes, you can bolt directly to the firewall per djmlambert's great pic (pro looking conversion!). Also note he's got 3/16" lines on the disk circuit and 1/4" lines on the drum circuit, just like the factory 71+ disk/drum set-up. A stock 71-72 combo valve would be perfect, or you can run an aftermarket adjustable prop valve - but you are correct in that the original distribution block from a 69 is not the correct valve for your soon-to-be-modified brake system. It appears you have the correct mc in your 1st post; assuming you purchased a manual brake mc (for disk/drum), it should have the deep hole in the rear piston (as opposed to the little shallow hole that accepts the short intermediate push-rod associated with a booster. Recommend check that your mc has a deep hole piston in the bore where it accepts the brake pedal pushrod. If it doesn't, i.e. just has a shallow little depression where the push-rod goes, then you may have a power brake mc (for disk/drum).

[54blackhornet]

I sold my 71 gmc 1500 a few years ago. It came with non power discs up front. Master was mounted to the firewall just like in the photo above. It took me a few attempts to locate the proper NON POWER master, finally got it at Napa by going into the old paper parts books. Guy on counter was useless.

[Gregski]

Originally Posted by jocko

yes, you can bolt directly to the firewall per djmlambert's great pic (pro looking conversion!). Also note he's got 3/16" lines on the disk circuit and 1/4" lines on the drum circuit, just like the factory 71+ disk/drum set-up. A stock 71-72 combo valve would be perfect, or you can run an aftermarket adjustable prop valve - but you are correct in that the original distribution block from a 69 is not the correct valve for your soon-to-be-modified brake system. It appears you have the correct mc in your 1st post; assuming you purchased a manual brake mc (for disk/drum), it should have the deep hole in the rear piston (as opposed to the little shallow hole that accepts the short intermediate push-rod associated with a booster. Recommend check that your mc has a deep hole piston in the bore where it accepts the brake pedal pushrod. If it doesn't, i.e. just has a shallow little depression where the push-rod goes, then you may have a power brake mc (for disk/drum).

thank you so much for that detailed explanation, no where did it say if this was for manual or boosted, I was just happy to find one for disc/drum instead of drum/drum

I will check like you suggested

[Gregski]

Originally Posted by 54blackhornet

I sold my 71 gmc 1500 a few years ago. It came with non power discs up front. Master was mounted to the firewall just like in the photo above. It took me a few attempts to locate the proper NON POWER master, finally got it at Napa by going into the old paper parts books. Guy on counter was useless.

I hear that, I hate going to the parts stores on the weekends as they give the experienced Mon-Fri the weekends off and you are stuck with the new guy in the brand new NAPA shirt on

[72SB]

my 72 was manual disc/drum but I converted to power.

Here is a pic as it was with stock manual MC

[jocko]

Gregski, LMC used to carry manual vs power 71-72 master cylinders - here's a part # ref for you - https://67-72chevytrucks.com/vboard/...81&postcount=7

[54blackhornet]

Love your L6 with power steering !

[72SB]

Originally Posted by 54blackhornet

Love your L6 with power steering !

If its mine your talking about, yeah it is factory PS. I pulled the huge stock steering wheel and put in a smaller one as at 6'2" My leg was sideways to hit the brakes. Easy turning with the power with smaller wheel

Now power disc/drum brakes to....

[Gregski]

Originally Posted by jocko

It appears you have the correct mc in your 1st post; assuming you purchased a manual brake mc (for disk/drum), it should have the deep hole in the rear piston (as opposed to the little shallow hole that accepts the short intermediate push-rod associated with a booster. Recommend check that your mc has a deep hole piston in the bore where it accepts the brake pedal pushrod. If it doesn't, i.e. just has a shallow little depression where the push-rod goes, then you may have a power brake mc (for disk/drum).

I was able to stick a pen cap [Science] in that hole 1 1/2" deep would that make it the deep hole?


Some Specs


BrakeBest Select Brake Master Cylinder - New - NMC11339


Warranty: Limited Lifetime Warranty
Unit of Measure: Each
UPC: # 848074025655
New Or Remanufactured: New
Dust Boot Included: No
Number Of Ports: 2
Bore Size (in): 1.130 Inch
Reservoir Included: Yes
Bore Size (mm): 28.58mm
Reservoir Type: Integral
Number Of Pistons: 1
Sensor Included: No
Number Of Mounting Holes: 2
Gasket Or Seal Included: No
Bleeder Kit Included: Yes
Pedal Rod Included: No
Brake Booster Included: No
Port 1 Thread Size (Forward) (in): 1/2-20 Inch
Port 1 Thread Type (Forward): Inverted Flare
Port 2 Thread Size (in): 9/16-18 Inch
Port 2 Thread Type: Inverted Flare
Master Cylinder Body Material: Cast Iron

[HO455]

I don't know for sure about the master cylinders for manual disc brakes in our trucks, but I do know that in Pontiacs that the manual disc master cylinders were a one year only option and they had a different bore diameter than the power brake master cylinders did.

Last time searched for one I had to have the counterman look the number up in a BOOK! There was no listing in the computer for a manual master cylinder.

I would bet the bore diameters are different for our trucks also.

[Gregski]

Originally Posted by HO455

I don't know for sure about the master cylinders for manual disc brakes in our trucks, but I do know that in Pontiacs that the manual disc master cylinders were a one year only option and they had a different bore diameter than the power brake master cylinders did.

Last time searched for one I had to have the counterman look the number up in a BOOK! There was no listing in the computer for a manual master cylinder.

I would bet the bore diameters are different for our trucks also.

thanks, that sounds boring [sorry couldn't help it]

[dmjlambert]

Originally Posted by Gregski

I was able to stick a pen cap [Science] in that hole 1 1/2" deep would that make it the deep hole?

Yes that looks like a deep pushrod hole so it is for manual brakes. On our trucks the bore diameter is 1-1/8" for both manual and power brakes. Keith Seymore shared the engineering charts with us on what I think is the definitive thread about manual brake master cylinders for 71-72.

This is the same thread where 54blackhornet discussed his research at NAPA going into paper parts books to figure out the correct master cylinder.

http://67-72chevytrucks.com/vboard/s...30#post8909230

[72c20customcamper]

I used this master on my Studebaker to go from manual drum to manual disc .

https://www.speedwaymotors.com/GM-Co...ore,51673.html

Some pictures I used an inline portioning valve for the rear .

[jocko]

yep, 2nd the motion that you have a deep hole non-power brake mc - good news!

[Gregski]

and a few hours and a bucket of sweat later she's on

[Gregski]

hey bro, hey bro, what kinda carburetor are you running is that one of them organic Holley Carter Rochester Quadrajet Edelbrocks?

[dmjlambert]

Originally Posted by Gregski

hey bro, hey bro, what kinda carburetor are you running is that one of them organic Holley Carter Rochester Quadrajet Edelbrocks?

That's funny right there! Keep that truck organic!

[HO455]

I think they're called Quadrazaps.